1. Field of the Invention
Example embodiments of the present invention relate to photoresist compositions and to methods of forming a pattern using the same. More particularly, example embodiments of the present invention relate to photoresist compositions that may be used in the formation of a pattern in a semiconductor manufacturing process and to methods of forming a pattern using the same.
2. Description of the Related Art
In order to fabricate highly integrated semiconductor devices having high operational speeds, it has become necessary to form very fine patterns having line widths below about 100 nm. Conventionally, patterns are formed using a photolithography process which generally includes a photoresist coating process, an alignment process, an exposure process and/or a developing process.
The photoresist has a molecular structure that may be changed by light irradiated thereto, and a photoresist film is formed by coating a substrate including such a photoresist. A photomask on which an electronic circuit pattern is formed is arranged over the substrate where the photoresist film is formed by the alignment process. Then, an illuminating light having a particular wavelength is provided to the photoresist film so as to generate a photochemical reaction in an exposed portion of the photoresist film. Accordingly, a predetermined electronic circuit pattern may be transcribed onto the photoresist film by the alignment and exposure processes. The exposed portion of the photoresist film, which corresponds to the predetermined electronic circuit pattern, has an altered molecular structure. The photoresist film having the altered molecular structures is selectively removed by the developing process to thereby form a photoresist pattern on the substrate.
While the developing process is performed, the exposed portion of the photoresist film may be selectively removed from the substrate, or may selectively remain on the substrate. As a result, a photoresist pattern having a shape corresponding to that of the predetermined electronic circuit pattern is formed on the substrate. A minimal line width of the photoresist pattern is determined in accordance with a resolution of an exposing system. The resolution of the exposing system is determined by a wavelength of an illuminating light according to Rayleigh's equation as follows:R=k1λ/NA
In Rayleigh's equation, λ denotes a wavelength of the illuminating light of an exposing system, R denotes a resolution limit of an exposing system, k1 denotes a proportional constant of an exposing process, and NA denotes a numerical aperture of a lens of an exposing process. According to Rayleigh's equation, the wavelength λ of the illuminating light and the proportional constant k1 need to be as small as possible, and the numerical aperture of a lens needs to be as large as possible for decreasing the resolution limit of an exposing system. As the wavelength of the illuminating light becomes shorter, the resolution of the exposing system is improved and a line width of a photoresist pattern is reduced. Thus, the wavelength of the illuminating light, the exposing system and a resolution limit of a photoresist are essentially considered to form a fine photoresist pattern.
A photoresist is generally classified as either a negative photoresist or a positive photoresist. In an exposed portion of the positive photoresist, a blocking group of a photosensitive polymer is detached by an acid that is generated from a photoacid generator. The photosensitive polymer, from which the blocking group is removed, may be readily dissolved into a developing solution during the developing process.
A photoresist, which has been conventionally used for forming a pattern having a line width below about 75 nm, has a process margin that is insufficient for forming isolated and dense patterns. Accordingly, sparse patterns formed in a peripheral region have a critical dimension which is substantially different from that of dense patterns formed in a cell region. To overcome the difference in the critical dimension between the cell region and the peripheral region, a method of increasing an amount of a photoacid generator has been developed. When the amount of the photoacid generator increases, the above-mentioned problem may be solved, but a top portion of a pattern may be rounded or a damaged pattern may be formed.
Additionally, the photoacid generator having a hydrophobic property that poorly interacts with a hydrophilic resin in a photoresist composition, and thus the photoacid generator may not be uniformly distributed in a photoresist film.
FIG. 1 is a conceptional view illustrating a distribution of photoacid generators in a photoresist film formed using a conventional photoresist composition.
As illustrated in FIG. 1, the photoacid generators 14 poorly interacting with a resin 12 are not positioned adjacent to the resin 12, and are aggregated in a top portion of the photoresist film 10 formed on a substrate 5. Accordingly, a diffusion length of an acid generated in an exposure process and a baking process may become greater, and thus a photoresist pattern having a uniform profile may not be formed.